The invention relates to metal bodies such as auto catalyst supports having metal-to-metal diffusion and methods for forming same.
The automotive catalytic converter was introduced in the U.S. in about 1974. Since then, considerable advancements have been made. One of these improvements is the projected use of a metal-supported rather than ceramic-supported catalyst. The metal catalyst reduces both the volume and weight required to achieve the necessary catalytic efficiency. The metal supported catalyst, onto which the coating of alumina and precious metals is placed, is usually made by winding a suitable metal alloy with a flat and corrugated layer in a continuous concentric pattern.
A problem arises, however, in actual trial use where the layers telescope or extrude much like a collapsible cup. Once this occurs, the viability of the catalyst is lost.
It has become apparent that, in actual use, the metal supported catalyst will not remain intact simply under its own winding tension. Thus, it is necessary to try and arrest the tendency of the part to extrude. However, additional devices such as a simple retaining bar are not acceptable due to the added weight as well as pertubation of the gas flow.
As a possible solution to this dilemma, it has been proposed to fix the layers by a microplasma argon weld across the faces of the substrate. This welding process is an improvement, but it still is not a totally effective means to adequately prevent extrusion. Other problems associated with the welding process include the inherent difficulties associated with contacting the torch to the support and the optimization of suitable weld patterns to produce the desired effect. Therefore, there is a need in the art to develop improved techniques to prevent the extrusion and telescoping of metal auto catalyst supports.
As shown in FIG. 1, a corrugated metal sheet 10 has been laid upon a flat metal sheet 11 and the two sheets have been rolled together along the direction of arrow 12 to form cylinder 13. This cylinder 13 may be used as a metal substrate for an automobile catalyst. Notable features of this support include corrugated components 14, non-corrugated components 15, points e.g. lines 16 of contact between these corrugated and non-corrugated components and channels or open spaces 17.
The exposed surfaces 18 of corrugated and non-corrugated components are coated with a suitable e.g. precious metal catalyst to catalyze reactions in exhaust gas emissions flowing through channels 17.
One technique of applying the catalysts to the metal substrate is a wash-coating technique. According to this technique, since catalyst will not adhere sufficiently to the smooth metal surface of the support, a roughened alumina coat is applied to the substrate to promote adhesion of the catalyst. This roughened alumina coat may be obtained by first selecting as the composition for the components of the metal substrate an iron alloy containing aluminium. By heating this aluminium containing metal substrate in an oxygen containing atmosphere, Al.sub.2 O.sub.3 is generated at the exposed surface of the substrate. Then, the substrate may be washed with a slurry of alumina-in-water followed by heating to drive off the water and fuse the alumina to the surface of the substrate. The thusly washed-coated metal substrate is then further coated with the active catalyst composition.
Unless structural integrity is provided to the metal catalyst support, the wash-coat and catalyst may be scraped off the support. More particularly, referring to FIG. 1, if no means is used to adhere the components of the metal substrate together, the corrugated component 14 may be axially displaced or pushed-out from the non-corrugated component 15 by the force of exhaust gases running through the supported catalyst. As mentioned previously, welding together of the various components has been proposed to rectify this problem, but there are disadvantages with that technique.
The invention is founded on the observation that some adhesion between the components of the metal substrate results from heating of the substrate in an oxygen atmosphere to form Al.sub.2 O.sub.3 on the exposed surface of the substrate. More particularly, after such oxidation, when in order to destructively examine the product then under development a substrate was subsequently unwound, resistance to separating the layers was observed. The adhesion of the layers seemed to be a function of the winding tension, because adhesion was almost non-existent on the outer part of the substrate and the adhesion was observed to increase progressively towards the center. Accordingly, the oxidized metal surface components of the substrate tended to adhere to one another, much as a rusted bolt tends to fuse to the threads of the screw to which it has been joined. Furthermore, when contact areas were examined through a microscope, intermittent areas of bright fusion were observed.